1. Field of the Invention
The present invention relates to a sensor in a car window that is installed in a car window to detect an object to be detected that is located outside a car.
2. Description of the Related Art
FIG. 6 is a sectional view of a camera in a car window that represents a conventional sensor in a car window.
The camera in the car window includes a lens 1 provided on the inner surface of a windshield 3 (a windowpane), and a camera main body 2 serving as a sensor main body that detects, through the lens 1, an object to be detected (not shown) that is located outside the windshield 3.
In the camera in a car window, an upper incident ray 5, a middle incident ray 6, and a lower incident ray 7 from the object to be detected enter the lens 1 through the windshield 3, and the camera main body 2 photographs the object to be detected.
The camera in the car window, however, has been posing a problem in that a maximum optical path length L1 of the rays that directly enter the lens 1 through the windshield 3 is long. Reference character L1 in this case denotes the horizontal distance between the point at which the lower incident ray 7 exits from the inner surface of the windshield 3 and the center line of the lens 1.
Furthermore, when the rays enter the lens 1 through the windshield 3, ghost rays 11 reflected off of a dashboard or the like reflect on the windshield 3 and reach the lens 1 along the same optical path taken by the upper incident ray 5, the middle incident ray 6, and the lower incident ray 7, thus forming an image on the dashboard or the like. This has been presenting a problem in that the image formed on the dashboard is undesirably superimposed on the image of the object to be detected, leading to deteriorated quality of the photographed image.
To solve the problem, there has been adopted a means for covering the area between the camera main body 2 and the windshield 3 by a hood 9 shown in FIG. 7 thereby to block the ghost rays 11 reflected off of a dashboard or the like, as disclosed in, for example, Japanese Unexamined Patent Publication No. 4-194827.
In recent years, however, there has been a trend toward increasing the angle of inclination of the windshield 3 to reduce air resistance. The trend has inevitably resulted in an increase in the optical path distance L1 with a consequent increase in the size of the hood 9. This has given a rise to a problem in that the visual field of occupants is interfered with, and a camera in a car window cannot be installed at a proper position free of the interference by a rearview mirror 12.
The present invention has been made with a view toward solving the problem described above, and it is an object of the invention to provide a sensor in a car window, the sensor primarily featuring a reduced maximum optical path distance from a windowpane to a lens so as to permit a reduction in the size thereof.
To this end, according to the present invention, there is provided a sensor in a car window, the sensor having a lens that is provided on the inner side of a sloping windowpane to condense light coming from an object to be detected that is located outside the windowpane, a sensor main body that detects the object to be detected by means of the light that has passed through the lens, and a transparent member that is provided between the windowpane and the lens to refract the light from the object to be detected that has passed through the windowpane.